Classic Motorcycles History
The first V-Twin offered by Harley-Davidson was the D Model, produced from 1929 to 1931. The R model, made from 1932 to 1936, began Harley's side-valve tradition in the 45-cid class. The D and R models were succeeded in 1937 by the W series.
Advantages of a flathead (side-valve) engine over an overhead valve engine were cost of manufacture and simplicity. With valves positioned in the engine block beside the piston (instead of in the cylinder head, as in an OHV engine), pushrods and rocker arms were not needed. Additionally, cylinder heads need only be a simple casting with threaded holes for the spark plugs.
During the years 1940 through 1945, Harley-Davidson built over 60,000 side-valve motorcycles for the U.S. and Canadian Armies.
Starting in 1932, the 45-cid side-valve engine powered the Harley-Davidson Servi-Car, whose many uses included police bike, mail carrier, and tow vehicle. Although never selling in large numbers, the three-wheeled Servi-Car stayed in production until 1973, with several reportedly built in 1974.
45-cid Harley flatheads look similar to the Big-Twin Harleys. The easiest way to tell them apart is Big-Twins have their drive chain on the left, the 45's are on the right.
Harley-Davidson's Ironhead Sportster is arguably the loudest and meanest-sounding V-twin ever. Produced from 1957 to 1985, sales increased nearly every year, along with improvements in power, handling, and reliability.
The Sportster's unique sound while idling is a consequence of it's uneven firing pattern. After the rear cylinder fires, the crankshaft completes 405 degrees of rotation before the front cylinder fires, then 315 degrees of rotation until the back cylinder fires again.
This uneven power stroke does cause vibration, which is certainly noticeable sitting on a thinly-padded seat, atop an engine which is bolted directly to the frame. Many riders disregard this, claiming the solid engine-mount enhances a bike's road feel.
The multi-cylinder motorcycle years started in 1968, with the three-cylinder Triumph Trident , followed quickly by Honda's CB750-4 in 1969.
First Six-Cylinder Motorcycle
Both automobile and motorcycle manufacturers have experimented with six-cylinder engines since at least the 1920's.
In 1964, Honda produced the first of several RC-series bikes, a 24-valve, straight-six cylinder motorcycle made exclusively for GP racing. It's 249cc size was made from a 39mm bore and a 34.8mm stroke.
Honda's RC166, produced in 1966, was also 249cc, but used a bore and stroke of 41 mm and 31 mm. The following year saw the 249cc RC167, followed by the 297cc RC174 (41 mm and 37.5 mm) which raced in the 350cc class. The Honda RC-series bikes were never offered for sale to the public.
The first and smallest-sized production straight-six cylinder motorcycle was the Benelli 750 Sei, which displaced 747.7 cc. Benelli's 750 Sei was the world's first production six-cylinder motorcycle.
Japan's Six-Cylinder Bikes
Benelli had surpassed the Japanese in multi-cylinder bikes, until 1978, when Kawasaki introduced their six-cylinder bike, the KZ-1300. The KZ was a complex, sophisticated machine, weighing over 700 pounds, with an output of 120-horsepower and 85 ft/lb of torque. Road tests of the era showed the big Kaw topping 140 mph, with quarter-mile times under 12 seconds. The following year, Honda introduced their six-cylinder bike, the twin-cam, 24 valve CBX-1000. At 600 pounds, the CBX was lighter than the KZ, producing a smooth 105-horsepower, and had recorded 11.36 seconds in the quarter-mile. Both the KZ and the CBX morphed into sport/touring bikes.
Offering the allure of litre-bike performance in a mid-size package, all of Japan's Big Four offered turbocharged bikes in the Eighties. As more power was coaxed out of naturally-aspirated engines, the more expensive and complex turbos fell out of favor, with 1985 being the last year a production turbocharged motorcycle was offered for sale in the U.S. The quickest of these bikes was the Kawasaki GPz-750 Turbo.
Classic Sports Bike Gallery - Sport bikes from the 50s, 60s, 70s, and 80s.
Classic Motorcycle Resources - Links to parts, tools, accessories, etc.